Tracking radars used in special carrier vehicles enable these vehicles to home in on a given target. The presence of an off-target jammer, i.e. a jammer which is not carried by the target itself, is intended to prevent the carrier from reaching its target. These devices are particularly troublesome where they consist of active jammers which emit a very strong, continuous signal modulated in frequency in the frequency range generally used by the homing-type guidance systems. The signal emitted by the jammer does not bear any definite phase or amplitude relationship with the signal generated by the radar of the guidance system and reflected by the target. The guidance systems normally employ tracking radars comprising an antenna which supplies an amplitude or phase zero in a given direction known as the antenna axis. The antenna of this type of radar is associated with a receiver which comprises on the one hand a directional-error or difference channel .DELTA., delivering a signal proportional to the amplitude or phase difference between the signals generated for directions of wave propagation other than that of the axis of the antenna, and on the other hand a sum channel .SIGMA. delivering information relating to the signal strength received from both the jammer and the target. On account of the presence of the jammer radiation, the resulting signals are fluctuating and the guidance system is incapable of exploiting the information emanating from the weakest source, namely the target.